If you ask most people to name a high quality piano, most would probably say Steinway, and rightly so because they certainly are one of the best pianos made. (http://www.steinway.com/)
But there are a few others who are just as good if not better.
To name a few great piano makers one could name the Italian maker Fazioli and the Great Canadian pianist Angela Hewitt has recently switched from Steinway to Fazioli. (http://www.fazioli.com/eng/index.php)
Then there are the Great German Piano makers. Germany produces most top quality pianos today and of course German craftsmanship is legendary.
The American maker Mason & Hamlin produced legendary pianos in the early part of the 20th century but stopped being a top maker in the great depression, but they have recently started again to make top pianos which are based on the legendary early models. (http://www.masonhamlin.com/)
Like all the above mentioned pianos Bösendorfer shows great attention to every detail in the making of its pianos but they, unlike other manufactures make the case of the piano an extension of the soundboard so the tone is sweet, rich, fat and creamy.
Famous Bösendorfer users include Oscar Peterson, Paul Badura Skoda, Tori Amos, Andre Previn, Garrick Ohlsson, Paul Bley, Andras Schiff, Cecil Taylor and many more and the worlds most famous Pianist the legendary Franz Liszt used Bösendorfer and highly praised them.
I don´t own a Bösendorfer but was lucky enough to play one for a time at my music school here in Reykjavik, also a friend of mine owns a Bösendorfer Grand and it is always a treat when I visit him to sit at this marvelous music machine and have a Grand time indeed.
The only problem with high quality items like this is of course the price, they are very expensive but as always quality does not come cheap.
If you are thinking about buying a piano or is interested in Piano makers you must get the Piano Book by Larry Fine, written by a piano technician and it is constantly uppdated, this book is a mine of information on pianos.
The youtube links below of course do not give justice to the fabulous sound of the Bösendorfer.